The magnetic property measurement is an indispensable means in the study of the physical properties of magnetic materials and superconducting materials. As regards this magnetic property measurement, the machine made by Quantum Design Corp. of the US and called MPMS (Magnetic Property Measurement System) is in fact monopolizing the market as a standard measurement system. This system has two distinctive features, i.e. the realization of high sensitivity owing to the use of a Superconducting QUantum Interference Device (SQUID) and the automatic acquisition of data owing to the perfect automation of measurement.
Since the lower limit of the measurement temperature of this system, however, falls no further than 1.8 K that is a magnitude attained by pumping on liquid helium 4, the system has been unusable for the study of Ru-based and Re-based superconducting oxides, various heavy-electron type superconducting materials, organic magnetic materials and molecular magnetic materials which have lower transition temperatures than this lower limit.
In the invention of JP-A 2002-248325 (“magnetic property measurement system utilizing a helium 3 refrigerator”), a means that is enabled by the refrigerating effect utilizing liquid helium 3 to produce in the specimen chamber of the MPMS a space cooled till 0.3 K and permit magnetic property measurement at temperatures ranging from 0.3 K to 1.8 K is revealed.
Specifically, FIG. 2 is a diagram schematically illustrating the structure of a helium 3 refrigerator-utilizing magnetic property measurement system formerly proposed by the present inventor and depicting the software configuration of a controlling device for the magnetic property measurement system as well. As the basic structure of the helium 3 refrigerator-utilizing magnetic property measurement system shown in this diagram, a magnetic property measurement system 1 utilizing a main structural component of the system heretofore widely used under the name of MPMS as described above is used. In this system, a liquid helium container 2 disposed therein allows such a helium 3 refrigerator 20 as will be specifically described herein below to be mounted thereon via an opening formed in the upper part thereof and this helium 3 refrigerator 20 allows insertion therein of a sample rod 5 in a similar manner to that heretofore used for the EMS.
The basic function as a measuring device of this magnetic property measurement system 1 consists in enabling a micromagnetic field generated by a magnetic sample fixed to the sample rod 5 to be detected with a SQUID that makes use of the Josephson effect of a superconducting junction and consequently enabling measurement of the magnetic susceptibility and magnetization curve of a magnetic material and the Meissner effect of a superconducting material sample.
The more specific structures of the magnetic property measurement system 1, the helium 3 refrigerator 20, etc. mentioned above are described in detail in the specification of the former patent application and will be omitted herein. In outline, a cylindrical outer tube 6 is suspended into the liquid helium container 2 holding a liquid helium 4 via an upper opening thereof and is provided on the lower end face thereof with a slender tube 7 extended and opened into the liquid helium 4 stored in the liquid helium container 2.
This outer tube 6 is extended outwardly above the liquid helium container 2, provided on the lateral part thereof with a pump-connecting opening 19, and adapted to connect to the pump-connecting opening 19 via a pipe 10 a main pump 9 of the sort commonly provided for the conventional MPMS. Further, in this system, an auxiliary pump 11 is connected to the pipe 10 as illustrated in FIG. 2. As described herein below, the system enables the interior of a sample chamber 12 to be brought to a still lower temperature by operating this auxiliary pump 11 in addition to operating the main pump 9.
The outer tube 6 is provided on the inner side thereof with a cylindrical sample chamber inner tube 8 that has formed in the upper terminal part thereof an opening for mounting a sample. Directly below the opening, there exists a valve for shutting a measuring space off the atmosphere, a drive mechanism 33 adapted to catch the partly bulged part of the sample rod and move the sample rod vertically, and other necessary parts. Further, the opening for mounting the sample is adapted to form tightly sealed connection to a lower terminal opening 17 of a box 16 through a seal member 18 such as an O-ring compression fitting that excels in sealing performance.
The sample rod 5 which has fixed in the lower part thereof a plurality of measuring members 21 including a sample piece, a heater and a temperature sensor is enabled by opening a lid 36 of the helium 3 refrigerator 20 to be inserted into a main pipe 23 via an opening 24 formed for mounting the sample rod in the upper terminal part of the main pipe 23 and mounted therein. Incidentally, when the sample rod 5 has been inserted into the main pipe 23 as described above, it can be thoroughly sealed with the seal member like an O-ring face seal that is disposed in the opening 24 part for mounting the sample rod. In the illustrated example, the main pipe 23 is provided on the lower periphery thereof with an insulated vacuum member so as to insulate the interior of the main pipe 23 from the space of the sample chamber 12 existing on the external side thereof.
The helium 3 refrigerator 20 uses a bellows 28 to interconnect the opening formed in the upper lateral wall of the main pipe 23 and the opening in the lateral wall of the box 16 and uses a helium 3 gas handling system 30 to first evacuate air in the main pipe 23, introduce helium 3 into the main pipe 23 and pump on the liquefied helium 3. Incidentally, the helium 3 gas handling system 30 and the opening 27 are interconnected with a pipe 31 and the pipe 31 is provided with a valve 32 halfway along the length thereof.
In the system that is provided with the helium 3 gas handling system 30 as described above, the detection by the SQUID is effected by rendering the main pipe 23 movable relative to the box 16, and consequently enabling the main pipe 23 to be vertically moved by a moving device 33 relative to the box 16 fixed on the outer tube 6 of the magnetic property measurement system 1, thereby moving the sample through the pickup coil wound on the outer periphery of the outer tube 6 to generate a current proportional to the magnetic moment of the sample.
A signal wire 34 is extended inwardly from a lateral wall 26 of the box 16 and, when the sample rod 5 is inserted into the main pipe 23, joined to a connector that is disposed in the upper terminal part of the sample rod 5. As a result, the signal wire 34 makes it possible to transfer signals with a control device 40 for use in the magnetic property measurement system as illustrated in FIG. 2. Incidentally, the magnetic property measurement system 1 is also enabled to form connection to the control device 40 of the magnetic property measurement system with the object of effecting control of magnetic field and control of temperature in the interior thereof.
The control device 40 for the magnetic property measurement system, as illustrated in FIG. 2, can be operated by using the MV (MultiView) software 41 already existing heretofore as a unit of software for controlling the magnetic property measurement system 1. In this invention, a software 42 indicated as I-Helium 3 in the diagram is used additionally for the purpose of measuring magnetization of helium 3 in a temperature range of 0.3 to 2 K by the use of the sample refrigerator 20.
By this i-Helium 3 software 42, the transfer of input and output with the temperature sensor and heater on the sample rod 5 can be individually and directly carried out. Further, for the purpose of enabling this magnetic property measurement system to perform a prescribed operation, the operator thereof is enabled to feed in advance the system with a measuring-sequence input 43 as a set of commands to take full control of measurement. As a result, the command of the i-Helium 3 software during the course of the measurement causes the MV software 41 to function through the HSP software 47, widely used for external control of applications and consequently enables the capability of the MV software 41 to control the magnetic field in the magnetic property measurement system 1, and process the input signal of the measurement to calculate the magnetization of the sample.
In the system of such a configuration as described above, after the main pipe 23 has been evacuated to a high vacuum with the helium 3 gas handling system 30 through the opened valve 32, the main pump 9 is actuated by dint of the function of the MV software 41 that is a control software for the MPMs in the control device 40 for the magnetic property measurement system, in order to cool the sample space 12 to 1.8 K. Here, the temperature of the sample space can be further lowered to about 1.5 K by additionally putting the auxiliary pump 11 formed as of a rotary-vane pump to operation.
In the resultant state, when the helium 3 gas (3He gas) is introduced into the main pipe 23 via a liquid nitrogen trap by the operation of the helium 3 gas handling system 30, the helium 3 gas is liquefied and retained in the lower part of the main pipe 23. After the liquefied helium 3 gas so retained has totaled to a prescribed amount, the environment of the sample attached onto the lower terminal part of the sample rod 5 is enabled to be maintained at a low temperature of 0.3 K by evacuating the helium 3 gas from the main pipe 23 with a closed evacuating system by the operation of the helium 3 gas handling system 30. Thereafter, the operator is enabled to utilize the system for acquiring data by dint of the function of the measurement software of the MPMS while controlling the temperature of the sample and the magnetic field as occasion demands.    Patent Document 1: JP-A 2004-087899